A hydrostatic rotary cylinder machine of this type is disclosed in EP 1 074 740 B1. An advantage of the formation of a rotary cylinder machine disclosed there over earlier solutions is that the roller bearings of that part of the shaft which is under high hydrostatic load are arranged directly adjacent with a small axial spacing in the stationary housing so that a very small degree of bending deformation and tooth deformation on the shaft and accordingly a very high degree of thrust and hence of torsional output are achieved. Since, owing to this bearing arrangement, there is no possibility of providing a 1:1 rotary connection between the rotary piston acting as a rotor and the rotary valve responsible for the commutation, it has been proposed to drive the rotary valve synchronously via a toothed gear from the shaft. In the known embodiment, this toothed gear is an eccentric internal gear in which the disk-like rotary valve itself acts as an eccentric member of this gear and hence executes an unavoidable orbital movement. However, comprehensive experiments have shown that this concept which initially appears striking cannot be realized in practice at high operating pressures because the necessary eccentric movement of the rotary valve relative to the stationary control panel does not permit sufficiently accurate commutation of the machine. Greatly varying torque output at the shaft, unsatisfactory volumetric efficiency and loud noises are the result since the outer part of the eccentric gear must operate in the high pressure range. Furthermore, the axial compensation of the hydraulic forces acting axially on the rotary valve by the compensating piston was not optimal owing to the eccentric movement of the rotary valve.
Since the tooth systems of the eccentric gear produce a displacement effect similar to that in the case of an internal gear pump, it is unfavorable, owing to the hydrostatic losses resulting there, if this displacement takes place in the high-pressure part of the machine.